Once wtmpx hits 2 GB in size Solaris slows down. You can setup a logadm to rotate the log once every two weeks:

~# logadm /var/adm/wtmpx -C 2 -c -p 6m

  • -C number of copies to keep
  • -p time between each log cycle (6 month)
  • -c copy and them truncate (doesn’t need to restart a service then)
  • -w writes an entry into /etc/logadm.conf for this log file

The like to add to  /etc/logadm.conf

/var/adm/wtmpx -C 2 -c -p 6m

Otherwise, you can go through a series of commands to backup the file manually and overwrite it with a clean one. This was likely the sequence used pre Solaris 9 days when logadm came into the picture.

~# cd /var/adm/
~# /usr/lib/acct/fwtmp < wtmpx > wtmpx.a
~# cp wtmpx.a wtmpx.a.bak
~# cat /dev/null > wtmpx.a
~# /usr/lib/acct/fwtmp -ic < wtmpx.a > wtmpx